1. Field of the Invention
This invention relates to material handling industrial trucks and is particularly suitable for an industrial truck which includes a mobile frame having a centrally located mast or upright structure upon which a load carriage is mounted for lifting and lowering movement. The load carriage may include an operator's station which moves upwardly and downwardly with the load.
2. Description of the Prior Art
The industrial truck mentioned is the non-counterbalanced or straddle type. The frame extends sufficiently to the front and rear of the mast structure, and laterally, to provide stability. At the front of the machine the frame may be equipped with caster wheels near the outer edges together with a centrally located steerable traction wheel to provide propulsion and braking. At the rear of the vehicle unidirectional wheels are located on outrigger portions of the frame which are sufficiently long and spaced apart to afford stability.
It is known also to assemble a counterbalanced type industrial truck from some of the same sub-assemblies or modules as are used for the already described straddle type. In the counterbalanced type industrial truck the frame is shortened at the rear and the caster wheels at the front are omitted. Then, if the drive wheel is properly secured with respect to the frame, a counterbalanced type industrial truck can be produced from some of the same modules used in the straddle type industrial truck.
U.S. Pat. No. 3,756,350 Gandolfo et al, dated Sept. 4, 1973, discloses industrial truck modules which can be assembled to form either the straddle type or the counterbalanced type industrial truck described in the preceding two paragraphs. The industrial truck shown in FIGS. 1, 3 and 5 of that patent is the straddle type while that shown in FIGS. 2 and 4 is the counterbalanced type.
In the Gandolfo et al patent the power module includes the storage battery which provides energy for operating the industrial truck, along with a propulsion motor and drive unit, and a second motor for driving a hydraulic pump that serves to raise and lower the movable mast and actuate other devices. Also the electrical traction controls and the hydraulic supply tank are located in the power module along with the necessary electrical and hydraulic connections.
In the foregoing patent the entire power module is pivotally mounted in order to accommodate the drive wheel, which is the fifth wheel of the industrial truck, to the floor or road surface with sufficient force to provide adequate traction and braking. The power module is pivotally mounted on a transverse horizontally disposed axis in front of the mast structure.
U.S. Pat. No. 2,643,740 Quayle, dated June 30, 1953, discloses a five wheel straddle type truck with a similar pivoted power module except the pivot axis is rearwardly of the mast. The bottom of the hydraulic ram which operates the lift mechanism on the mast rests on the pivoted structure so that the force on the traction wheel varies responsively to the weight carried on the mast of the industrial truck. In Quayle as in Gandolfo et al the entire power assembly including the battery, traction wheel and motor, hydraulic reservoir and pump, and other components are included in the pivoted power module.
U.S. Pat. No. 3,515,233 Stammen, dated June 2, 1970, shows a straddle type industrial truck in which the power module moves with respect to the frame by sliding on the mast instead of pivoting, and tension springs are provided on each side of the mast structure to transfer part of the weight of the power module to the frame leaving only a portion of it on the drive wheel.
It is known to construct a five wheel straddle type industrial truck similar to those shown in the Gandolfo et al and Quayle patents in which the pivotally mounted power module includes the battery along with the traction wheel, motor and gearing, but, does not include the hydraulic reservoir and pump.
Stability of the industrial truck plus the smoothness and ease of operating it over the floor are important in industrial trucks of the type under discussion, particularly since the operator may be elevated on the load carriage. One of the most important elements affecting these characteristics is the storage battery which is utilized to propel the vehicle. Such a battery in a typical vehicle of this type may vary from about 1,000 lbs. (450 kg.) to about 2,000 lbs. (900 kg.). Such a variation can occur for a single industrial truck because of the availability of a different size battery while the regular battery is being recharged, for example. Also an industrial truck of this type may be operated under some circumstances without any battery by the use of jumper cables typically used to move the truck during maintenance or to operate the truck in applications where the truck is used in fixed guidance path(s) using a remote power source (possibly rectified alternating current) to the truck through flexible power cables.